1. Field of the Invention
The present invention relates, in general, to a cooling device for microwave ovens with a halogen lamp and, more particularly, to a cooling device designed to allow a cooling air current passing along both a light reflection plate and a lamp protection filter.
2. Description of the Prior Art
As well known to those skilled in the art, a variety of cooking devices have been proposed and used. Of the cooking devices, the primary one is cooking ware, which is designed to have a shape suitable for containing food therein and is laid on a heater so as to be directly heated by the heater while cooking.
In addition, several types of electric cooking devices, designed to directly or indirectly utilize electric power while cooking, have been proposed and used. An example of conventional electric cooking devices is a microwave oven using a magnetron as a heat source. In such a microwave oven, the magnetron is electrically operated to generate microwaves and applies the microwaves to food in a cavity, thus allowing the microwaves to cause an active molecular motion in the food. Such an active molecular motion in the food generates molecular kinetic energy, thus heating and cooking the food. Such microwave ovens are advantageous in that they have a simple construction and are convenient to a user while cooking, and easily and simply heat food in the cavity. The microwave ovens are thus somewhat preferably used for some cooking applications, such as a thawing operation for frozen food or a heating operation for milk requiring to be heated to a desired temperature.
However, such microwave ovens also have the following problems. That is, the ovens have a defect in their heating style in addition to limited output power of the magnetron, and so it is almost impossible to freely or preferably use them for a variety of cooking applications, without limitation. In a detailed description, the conventional microwave ovens only utilize a magnetron as a heat source, thus undesirably having a single heating style. In addition, the output power of the magnetron, installed in such ovens, is limited to a predetermined level. Therefore, the conventional microwave ovens fail to provide a quick and highly effective cooking operation. During a cooking operation utilizing such a microwave oven, food in a cavity is heated at its internal and external portions at the same time, and this may be an advantage of the oven in some cases. However, such a heating style may result in a disadvantage while cooking some food. For example, the cooking style of the conventional microwave ovens is not suitable for cooking pizza for reasons that will be described in more detail later herein. Another disadvantage, experienced in the conventional microwave ovens, resides in that the ovens exceedingly remove moisture from food.
In an effort to overcome the above-mentioned problems, several types of microwave ovens, having another heat source in addition to a magnetron, have been proposed and used. For example, a microwave oven, having a convection heater in addition to a magnetron in a casing and originally designed to be used for a variety of cooking applications, has been proposed. However, such a convection heater only acts as a single heat source, thus failing to allow the microwave oven to have a variety of operational functions.
In a brief description, the conventional microwave ovens are problematic in that they have a single heating style utilizing microwaves, limited output power of a magnetron, and cause the evaporation of an exceeding amount of moisture from food. The microwave ovens, having another heater in addition to a magnetron, fail to completely overcome the problems experienced in the conventional microwave ovens.
In order to solve the problems of the conventional microwave ovens, another type of microwave oven, utilizing a light wave, has been proposed. In this microwave oven, a lamp, wherein at least 90% of the radiation energy has a wavelength of not longer than 1 .mu.m, is used as the additional heat source. In said microwave oven, both visible rays and infrared rays from the lamp are appropriately used, and it is possible to preferably heat the exterior and interior of food while making the most of characteristics of the food. An example of such a lamp is a halogen lamp.
Due to a difference in wavelengths between the infrared rays and visible rays emanating from a halogen lamp, the heating styles for the exterior and interior of food are different from each other. While cooking pizza utilizing a halogen lamp, it is possible to appropriately heat the pizza in a way such that the exterior of the pizza is heated to become crisp and the interior is heated to be soft while maintaining appropriate moisture.
FIG. 1 is a conventional microwave oven utilizing a halogen lamp as an additional heat source. As shown in the drawing, the microwave oven comprises a halogen lamp 12 installed on the top wall 10 of a cavity 2. The microwave oven uses the light waves, radiated from the lamp 12, for heating food in the same manner as that described above, with the characteristics of the light waves remaining the same as that described above.
A light reflection plate 14 is installed at a position above the halogen lamp 12, thus reflecting any light waves, emanating upwardly from the lamp 12, back downwardly into the cavity 2. A plurality of light transmitting holes 16 are formed on the top wall of the cavity 2, with the halogen lamp 12 being held on the top wall.
The microwave oven also has a device for cooling the halogen lamp 12. The detailed construction of a typical cooling device for the halogen lamp 12 is shown in FIG. 2. As shown in the drawing, the typical cooling device comprises a cooling fan unit 20 installed on the top wall 10 of the cavity 2 at a position around the light reflection plate 14. The cooling fan unit 20 is designed to allow a cooling air current, radiated from the unit 20, to pass over the top wall 10 of the cavity 2. The air current thus cools the parts installed on the top wall 10 of the cavity 2.
A mesh member 15, having the light transmitting holes 16, is installed under the halogen lamp 12, which is positioned under the reflection plate 14. The above mesh member 15 allows the light, radiated from the lamp 12, to pass into the cavity 2 through the holes 16. The member 15 also prevents the microwaves from being undesirably led from the cavity 2 to the lamp 12 and from damaging the surface of the lamp 12.
A lamp protection filter 18, made of a light transmitting material, such as glass, is provided on the top wall 10 of the cavity 12. The objective of the protection filter 18 is to protect the halogen lamp 12 from impurities, such as steam and/or oil smoke, rising from food during a cooking operation.
The above cooling device is problematic as follows.
During a cooking operation, the lamp protection filter 18 is heated to a high temperature, for example, about 800.degree. C. to 900.degree. C. However, the cooling device is free from any means for cooling the protection filter 18. Also the impurities, or the steam and oil smoke emanating from food while cooking, are adhered to the filter 18. However, the cooling device lacks of means for protecting the filter 18 from such impurities. When the impurities are adhered to the filter 18, the light transmissivity of the filter 18 is reduced, thus undesirably lengthening the heating time for food and reducing the expected life span of the halogen lamp 12.